X-Ray imaging is important for diagnostic and interventional procedures, but comes with many risks to the patient and staff. The medical industry is striving to find solutions to minimize radiation exposure during such procedures. One of the best ways to minimize the radiation exposure is to filter the x-ray beam outside of the region of interest (ROI). X-Ray attenuation filters are usually made of thin metal plates, such as lead, steel or aluminum.
Salient features such as anatomical features or tool tips will move during any procedure. If the filtering mechanism has a static aperture, the user requires a longer exposure to reposition the patient table.
An x-ray image benefits from high levels of radiation exposure for several reasons. High energy level x-ray beams are less likely to be attenuated by hard tissue, allowing tissue such as bone to be imaged. A higher X-ray beam energy greatly reduces signal-to-noise ratio in low exposure images. The contrast and image exposure is also reduced in low energy x-ray images, making it difficult to discern features. Background regions, ie. regions that do not contain salient features, do not need to have the same image quality and, therefore, the user can sacrifice the image quality to reduce their exposure to harmful ionizing radiation.
There are three types of x-ray attenuation devices that are designed to select an area of interest. The first type has a continuously variable attenuation profile with a continuously variable position. An example of this method is demonstrated in U.S. Pat. No. 8,693,628. This type is typically expensive to build and requires many heavy moving parts. The second type has a fixed size with a variable position, such as U.S. Pat. No. 5,278,887 and US Application 2015/0023466. This second type cannot typically be adjusted in terms of shape and size, limiting the ability of these devices to reduce radiation exposure. The third type has a variable aperture size, but cannot vary the position. These are the most common types of collimators and attenuation devices, examples are U.S. Pat. Nos. 5,881,127, 4,868,843 and 4,489,426. All three types typically limit the user to one aperture shape, such as a rectangle or a circle.
The disclosed invention a method of reducing radiation exposure using a set of fixed of apertures or filters with varying attenuation profiles. The preferred embodiment selects one of the fixed apertures or filters and positions it in the image area using rotary actuators. This method provides the flexibility of multiple attenuation profile shapes and sizes, while also allowing the user to position the attenuation profile around an area of interest. Another advantage of this invention is that the mechanism is sufficiently fast enough to repeatedly change position and attenuation profiles within one medical procedure, which is typically not possible with modern collimators, such as the type three devices described above.